Digital microfluidic platforms for automated chemical reactions

Microfluidic technology allows the miniaturisation and automation of chemical and biological processes. Specific advantages include the ease of process automation and integration, high analytical throughput, reduced sample and power consumption, increased speed and efficiency of reactions and system portability. Droplet-based microfluidics can be broadly categorised into 'conventional' channel devices or digital microfluidic (DMF) devices. The latter are also known as electrowetting-on-dielectric (EWOD) devices. Both platforms have distinct characteristics, with specific advantages and disadvantages when applied to chemical or biological analysis. High-throughput droplet manipulation is easily achieved with channel microfluidic devices, but it is hard to access individual droplets in this format. On the other hand, DM devices are designed for the manipulation of individual droplets in low-throughput. The bulk of the work in this thesis focuses on developing a complete platform for droplet manipulation using digital microfluidics. Extensive experimentation was undertaken to determine all relevant components of the device, including the composition of the dielectric layer, electrodes and hydrophobic layer. Once the optimum device had been constructed and tested, full automation of device function and droplet manipulation was achieved. Characterisation of on-chip droplet operations was subsequently performed. Special attention was given to droplet 'dispensing' and 'splitting'. Once the fabricated DMF devices had been fully characterised, three proof of principle experiments were developed to investigate the capabilities of DMF devices. To this aim, first a fluorescent dilution series was performed and characterised on-chip, second a peptide bond formation experiment was performed, and finally, iron oxide nanoparticle synthesis was performed on-chip. The integration of DMF devices with a miniaturised spectrometer was used to provide an on-line detection system. Channel microfluidic devices were also investigated with respect to the high-through-put creation of droplet interface bilayers (DIBs). Aqueous droplets containing lipids were formed in an oil carrier medium. As droplets were brought together a lipid bilayer was formed at the interface, creating an artificial membrane. This approach can be used as a platform technology to study trans-membrane proteins and drug-membrane interactions. Although there has been a lot of interest in this area, previous work has focused on the low-throughput formation of DIBs. The method developed here enables the formation of DIBs at rates in excess of 1 DIB per second.